The present invention relates generally to novel high amperage electrical switching or shunting apparatus. More particularly, the present invention concerns a liquid metal switch which is especially adapted for placement in a switching buggy used in a corrosive atmosphere of the type commonly found in close proximity to electrolytic cells used in the production of chlorine and caustic.
Chlorine and caustic are most commonly produced by the electrolysis of brine. The constructional features of the specific apparatus employed for this purpose vary, however, all such apparatus share the common feature that they require the usage of electric current. The vast majority of chlorine and caustic manufactured today is produced by the use of either the so-called diaphragm cell or the so-called mercury cell. In practice, a plurality of cells of a given type, often as many as a hundred or more, are usually located in a confined area, called a cell room, and are electrically connected in series. The resultant electrical arrangement of cells is commonly referred to as a circuit.
From a commercial standpoint, it is desired to operate the cell circuit in a continuous and uninterrupted manner. This means that when an individual cell in the circuit begins to exhibit undesirable operational characteristics, it must be repaired or removed from the circuit. In order to accomplish this while at the same time continuing the uninterrupted operation of the circuit, it is common practice to shunt the current around the affected cell while it is removed from the circuit for repair.
It has been common practice with low amperage electrolytic cells, i.e., those operating at about twenty to thirty thousand amperes, to employ an air cooled shunt or switch for the switching of the circuit around the affected cell. However, the recent trend in chlorine and caustic production has seen the introduction of new cell designs which are capable of operating at much higher amperage levels. Conventional air-cooled shunts and switches do not perform satisfactorily when used to shunt such high currents and therefore a new design has been necessitated.
A conventional liquid metal switch which has been developed for such higher amperage applications includes a sealed capsule in which a contact area is established between two fixed contact surfaces via a moving piston-shaped bridge contact. The bridge contact is electrically connected to a lower terminal only via a gallium-indium-tin liquid metal alloy for full current transfer. The bridge contact may be selectively electrically connected to an upper terminal contact member via the liquid metal such that at least a majority of the electrical current transfer is established through the liquid metal. It is a disadvantage of this type of liquid metal switch that the liquid metal used, i.e., gallium-indium-tin freezes at 11.degree. C. It is therefore frequently necessary to heat the switch before operating it. An electric cartridge type heater is provided with the switch to enable such heating to occur. Moreover, it is also a disadvantage of the known switch that the full current transfer between the bridge contact and the lower contact terminal takes place through the liquid metal since if the liquid metal drains from the switch the bridge contact will no longer be electrically connected to the lower terminal.
It has, therefore, been considered desirable to develop a new and improved liquid metal switch for use in electrolytic cell shorting applications, which would overcome the foregoing difficulties while providing better and more advantageous overall results.
A high amperage electrical switch according to the present invention includes a first terminal member including a piston chamber and a movable piston contact member located therein and a second terminal member. An insulating member is secured between the first terminal and the second terminal to prevent electrical contact therebetween unless the piston is in electrical contact with the second terminal member. At least one sliding contact current transfer means is provided on the movable piston member to continuously maintain a sliding contact between the piston assembly and the first terminal member. Actuating means are further provided for selectively moving the movable piston to establish electrical contact between said first and second terminal members.
A movable high amperage electrical switching apparatus adapted for use in a corrosive atmosphere according to the present invention includes a carrier housing assembly containing thereon spaced apart first and second electrical terminals. Electrical conducting means are positioned within the housing for selectively communicating with the first and second electrical terminals. At least one high amperage switch is provided on the chassis in contact with the conducting means. The switch includes a first switch terminal having a piston chamber and a movable piston contact member housed therein and a second switch terminal. The movable piston contact member is in continuous electrical contact with the first switch terminal and may be selectively actuated into electrical contact with the second switch terminal by the actuating means.
The principal focus of the present invention is the provision of an improved liquid metal switch assembly. An advantage of the invention is the provision of a switch assembly which is usable at all commonly encountered temperatures.
Another advantage of the invention is the provision of a switch assembly in which the contact piston is continuously maintained in electrical contact with its terminal by sliding contact current transfer means.
An additional advantage of the present invention is the provision of a series of such switches in a switch buggy.
Yet other advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.